Host–guest behavior of pillar[n]arene-based supramolecular assemblies

Pillar[n]arenes usually form 1:1 host–guest complexes with guest molecules. However, unique host–guest properties appear by the formation of new structures, such as tubular dimers, nanotubes, boxes, and end-capped cavitands. In addition, crystalline pillar[5]arenes show unique host–guest properties, such as gate opening, encapsulation of a guest molecule by two pillar[5]arene wheels, and quantitative uptake of alkane guest molecules. Therefore, cooperative binding of guest molecules to pillar[n]arene assemblies is the key to achieve unique host–guest behavior. Pillar[n]arenes show planar chirality owing to their shape, and thus coupling between the planar chirality and host–guest property enables planar chiral inversion, memory, and erasure. In this review, we discuss the diversity, functionality, and supramolecular chirality of host–guest pillar[n]arene assemblies.